1. Field of the Invention
This invention relates generally to control systems for multi-speed shiftable power transmissions such as are used in off-highway vehicles and other applications. In particular, this invention relates to an electronic transmission control system which controls the operation of an automatic transmission in relation to the operational conditions of such vehicles.
2. Description of the Prior Art
Prior art systems for controlling a multi-speed shiftable power transmission are complex and costly and require redundant circuitry to effect proper sequential operation of the solenoid valves normally used in such power transmission systems. Prior art electronic control systems for multi-speed shiftable power transmissions have been limited in the control functions they are able to effect and have also been susceptible to failure due to acceleration forces, shock vibration and environmental conditions to which they are exposed during actual use on earth moving machines, trucks, or other equipment.
Some prior art transmission control systems require a great deal of skill on the part of the operator, which increases the possibility of damage to the system due to incorrect operational procedures.
It is known in the art to use an electronic control system for shifting a power transmission which is suitable for use in an automobile; however, such control systems do not have the capability to control a transmission in response to the conditions encountered in heavy-duty use, such as in off-highway vehicles or earth moving equipment.